Studies are being conducted on the factors concerned with the stimulation of blood vessel formation of a series of transplanted tumors and tumor extracts using the hamster cheek pouch. A combination of electronmicroscopic and autoradiographic studies permit assessment of (a) the reality of the activity of the tumor extract and (b) the point of origin and the influence of some chemotherapeutic agents on the mode of action of the angiogenic factor in preventing or slowing the growth and invasiveness of the tumor are being conducted. A variety of materials including liver (dried and fresh), fibrin, hamster embryo and placenta, as well as tumors, have been investigated. Additional studies are in progress to compare vascularization patterns that occur in response to implantation of solid tumors with tissue culture preparations of tumors. BIBLIOGRAPHIC REFERENCE: Shubik, P., Feldman, R., Garcia, J. and Warren, B. A. (1976) Vascularization induced in the cheek pouch of the Syrian hamster by tumor and nontumor substances. J. Natl Cancer Inst., 37, 769-774.